Press brakes for bending sheet materials are provided with upper and lower tables opposed to each other that are supported by side frames, where the upper table or the lower table is made free to move upwards or downwards. The lower part of the upper table is provided with an upper tool holder for removably holding the upper tool, and the upper part of the lower table is provided with a lower tool holder for removably holding the lower tool, which cooperates with the upper tool. A bending process is then performed by inserting a sheet work material in between the upper tool mounted on the upper tool holder of the upper table and the lower tool mounted on the lower tool holder of the lower table.
Conventionally, the exchange of the upper and lower tools by dismounting and mounting the upper and lower tools of the upper and lower tables were carried out manually. The upper and lower tools includes divided tools divided into a plurality of elements and long tools, but the upper and lower tools are in general are heavy, and the dismounting and mounting in exchanging the upper and lower tools onto the table was a burdensome work.
Thus techniques to exchange the upper and lower tools by dismounting and mounting the tools relative to the upper and lower tables automatically have been developed. Related prior art references are JP55-45288, JP57-37408 and JPU63-21932. Also prior art references related to the tool of the present invention includes for example JP2771064 and the like.
Now in performing a bending process on a work by a press brake, there are cases where, for example, tools of different lengths are mounted separately at a plurality of locations on the tool holders of the upper and lower tables, and the bending process is performed on a workplace successively by the each processing station. The prior art references, however, all apply only to the case where there is only a single tool mounting location for the upper and lower tables and not for the case with a plurality of processing stations, and therefore the exchange of tools for the upper and lower tables with plural number of processing stations are still made manually.